In the prior art, there is a lens barrel provided with a first cylinder provided with a helicoid, and a second cylinder provided with another helicoid which is screw-engaged with that helicoid. In this lens barrel, the second cylinder is inserted into the inner portion of the first cylinder, and by making the helicoid of the second cylinder move along the helicoid of the first cylinder by rotating the second cylinder with respect to the first cylinder, the second cylinder extends with respect to the first cylinder. Further, at the inner face of the first cylinder, regions having a plurality of differing leads of the helicoid are provided, and the extension speed can be regulated with respect to the rotation angle (for example, refer to Japanese Unexamined Patent Publication No. 2006-113418).